Uranium is produced from uranium-bearing ores by various procedures which employ a carbonate or acid lixiviant to leach the uranium from its accompanying gang material. The acid lixiviants usually are formulated with sulfuric acid which solubilizes uranium as complex uranyl sulfate anions. The sulfuric acid normally is used in a concentration to maintain a pH between about 0.5 to 2.0. However mild acidic solutions such as carbonic acid solutions, having a pH between about 5.0 and 7.0 may also be employed. Carbonate lixiviants contain carbonates, bicarbonates or mixtures thereof which function to complex the uranium in the form of water-soluble uranyl carbonate ions. The carbonate lixiviants may be formulated by the addition of alkali metal carbonates and/or bicarbonates or by the addition of carbon dioxide either alone or with an alkaline agent such as ammonia or sodium hydroxide in order to control the pH. The pH of the carbonate lixiviants may range from about 5 to 10. The carbonate lixiviants may also contain a sulfate leaching agent. The lixiviant also contains a suitable oxidizing agent such as oxygen or hydrogen peroxide.
The leaching operation may be carried out in conjunction with surface milling operations wherein uranium ore obtained by mining is crushed and blended prior to leaching, heap leaching of ore piles at the surface of the earth, or in situ leaching wherein the lixiviant is introduced into a subterranean ore deposit and then withdrawn to the surface. Regardless of the leaching operation employed, the pregnant lixiviant is then treated in order to recover the uranium therefrom. One conventional uranium recovery process involves passing the pregnant lixiviant through an anionic exchange resin and the elution of the resin with a suitable eluant to desorb the uranium from the resin. The resulting concentrated eluate is then treated to recover the uranium values, for example, by precipitating uranium therefrom to produce the familiar "yellowcake."
The anionic ion exchange resins employed for uranium concentration are characterized by fixed cationic adsorption sites in which the mobile anion, typically chloride or another halide, hydroxide, carbonate or bicarbonate, is exchanged by the uranyl complex anion. Such anionic ion exchange resins are disclosed, for example, in Merritt, R.C., THE EXTRACTIVE METALLURGY OF URANIUM, Colorado School of Mines Research Institute, 1971, pages 138-147, which are hereby incorporated by reference. Suitable anionic exchange resins may take the form of polymers or copolymers of styrene substituted with quaternary ammonium groups or polymers or copolymers of pyridine which are quaternized to form pyridinium groups.
The adsorption of uranium from aqueous solutions is described by Merritt at pages 147-156, which are hereby incorporated by reference, where it is recognized that the presence of molybdenum in the pregnant lixiviant tends to reduce adsorption of uranium by the anionic ion exchange resin. Merritt discloses at pages 154, 163, and 164 that the presence of molybdenum in the pregnant lixiviant tends to poison the ion exchange resin, thus reducing the adsorption of uranium by the resin which results in decreased resin loading.